This invention relates to a corner brace for providing reinforcement between two similarly profiled tubular sections of a door frame, one adjoining the other at a mitre-angle of 45.degree.. More specifically, the present invention relates to a corner key structure which is forceably received within the tubular end portion of each frame member so as to provide reinforcement to the joint formed thereby.
The present invention is particularly adaptable to assembly in tubular metallic door frames such as employed in the construction of screen and storm doors wherein such a frame is relatively large in size but yet must include a rigid connection at the four corner joints thereof so as to operate effectively and maintain a planar, rectangular shape.
One of the problems encountered in prior art door frames and other similar types of structural frames such as found in large window constructions formed of metallic tubular sections, resides in joining the corners such as by welding the abutting ends of such framing sections into corner joints. Necessarily, it is desirable to provide such frame structures with a planar profile and squared corners. However, welding tends to distort the structures through expansion and contraction (with consequent warping and twisting) during and after welding, and hence it is extremely difficult to achieve perfect flatness and rectilinear form in the finished product. Also, it is difficult to meet rigid requirements of fire regulations as potentially applicable to fire window constructions wherein the welded corner joints would have to resist deformation and failure under the heat of a fire. Furthermore, welding procedures are time consuming and expensive as well as dependent on the welder's skill for the only partially uniform degree of form accuracy that is possible to obtain in welded structures.
The prior art also has considered different types of bolt actuated expansion braces for tubular members and for corner structures specifically. However, such structures suffer from undue complexity and limited adaptability other than for those specific frames for which they are designed.